Energy-based tissue treatment is well-known in the art. Various types of energy (such as electrical, ultrasonic, microwave, cryogenic, heat, laser, and/or the like) are applied to tissue to achieve a desired result. Electrosurgery involves application of high radio frequency electrical current to a surgical site to cut, ablate, coagulate, or seal tissue. Energy-based surgical devices typically include an isolation boundary between the patient and the energy source to isolate the patient from the potentially dangerous voltage and/or current levels. In monopolar electrosurgery, the active electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated. One or more patient return electrodes are placed remotely from the active electrode to carry the current back to the generator and safely disperse current applied by the active electrode. The return electrodes usually have a large patient contact surface area to minimize heating at that site. Heating is caused by high current densities which directly depend on the surface area. A larger surface contact area results in lower localized heat intensity. Return electrodes are typically sized based on assumptions of the maximum current utilized during a particular surgical procedure and the duty cycle (i.e., the percentage of time the generator is on).
Early types of return electrodes were formed as large metal plates covered with conductive jelly. Later, adhesive electrodes were developed with a single metal foil covered with conductive jelly or conductive adhesive. However, one challenge that arises from employing adhesive electrodes is that, if a portion of an adhesive electrode peels from the patient, the contact area of the electrode with the patient decreases, thereby increasing the current density at the adhered portion and, in turn, increasing the heating of the tissue at that location. This risks burning the patient in the area under the adhered portion of the return electrode if the tissue is heated beyond the point where circulation of blood can sufficiently cool the skin.
To address this problem various return electrode monitoring systems, generically called Return Electrode Contact Quality Monitors (RECQMs) or simply Return Electrode Monitors (REMs), have been developed. Such systems rely on measuring impedance at the return electrode to calculate a variety of tissue and/or electrode properties. These systems detect electrode peeling by identifying changes in amplitude of the impedance of the return electrodes. Prior REM systems, however, require expensive off-the-shelf and custom components that can be heavy and consume a relatively large amount of printed circuit board (PCB) area. Prior REM systems and methods also do not facilitate the measurement of an individual impedance of an interface between a patient and a single pad of a multiple-pad return electrode (such as a split-pad return electrode, for example), and/or the relative impedances of the respective interfaces between the patient and two or more respective pads of a multiple-pad return electrode.
In view of the above, there is a need for an improved system and method for return electrode monitoring that addresses the foregoing challenges and is able to communicate information across the isolation boundary between the energy source and the patient.